Three-Dimensional Numerical Simulation Of Dendritic Structure Of Hypoeutectic Al-Si Alloy

As a light alloy,aluminum(Al)alloy has been widely applied to construction,aerospace,civilian and war industr.Among them,Al alloy with fine-equiaxed grains has attracted more attention.And the change of initial composition content in Al alloy is a key factor affecting the grain refinement degree.In this paper,a three-dimensional sharp interface model was proposed by combining the cellular automaton(CA)method with the deterministic mesh anisotropy control(DMAC)algorithm.Through the experimental characterization and numerical simulation of the microstructure of as cast hypoeutectic Al-Si alloy,the accuracy of the model calculation simulation considering DMAC algorithm was verified;The growth characteristics and influencing factors ofα-Al dendrite and alloy structure were studied;The mechanism of Al-Si grain size changing with the silicon content of the initial alloy composition was explored and explained.First,the simulation accuracy of the model with DMAC algorithm added to a single α-Al dendrite was verified.The verification results showed that the threedimensional sharp interface model considering the algorithm could accurately calculate the interface curvature and reproduced the actual and reasonable dendritic morphology in a wide range of cooling rates.At the same time,the determination of the best parameters in the DMAC algorithm was explained accordingly.Then,the effects of grid size and undercooling on the growth of single dendrite were explored.The simulation results were as follows: the growth rate of dendrite was significantly accelerated with the increase of undercooling,and the branches of primary and secondary dendrite arms were more developed,and the results were consistent with the dendrite growth theory.Secondly,the dendrite structure of the alloy was simulated.First,the simulation calculation of alloys with different compositions was carried out by using the same nucleation undercooling parameters in theory,and then the differential scanning calorimetry(DSC)characterization experiment was carried out to determine the actual undercooling of alloys with different initial compositions,which was substituted into the CA model after considering the algorithm,and the growth process of dendritic structure was numerically simulated,To explore the similarities and differences between the two simulations and the characteristics and influencing factors of dendrite growth.The experimental and simulation results showed that the numerical simulation results under the same nucleation parameters were not consistent with the experimental trends.With the increase of Si content from3 wt.% to 10 wt.%,the undercooling degree of nucleation in the real world increases gradually;With the addition of initial Si content to 3 wt.%,the grain size decreased;When the Si content is greater than 3 wt.%,the grain size increased with the increase of Si content,which leaded to the coarsest structure of Al-10 wt.% Si,which was consistent with the trend of experimental results.With the increase of Si content,the Si poisoning effect was obvious in Al Si alloy.With the increase of Si content from 3wt.% to 10 wt.%,the degree of nucleation supercooling increased significantly.Therefore,the growth limiting factor Q had little effect on the transformation of grain size of alloys with different initial compositions,while the change of nucleation undercooling played a major role.Through the analysis combined with the interdependence model,it was also clear that Al-10 wt.% Si alloy was not easy to nucleate in the solidification process compared with the alloys used in other experiments,thus forming a broader invisible core area,so it had a coarser morphology.In this paper,DMAC algorithm and CA technology were combined to build a three-dimensional sharp interface model to overcome grid anisotropy,and experimental characterization and simulation methods were used to explain the influence of Si content in Al-Si alloy on grain size.The results will provide theoretical support and reference for 3D dendrite simulation and grain refinement of Al-Si alloy.